Methods and systems for stator cooling

ABSTRACT

A method of fabricating a stator for an electric motor is provided. The method includes providing a plurality of stator laminations. Each stator lamination of the plurality of stator laminations is a copy of the same stator lamination pattern. The method further includes stacking the plurality of stator laminations in a sequence along an axis, comprising periodically varying rotational orientations of the stator laminations in the sequence. The method further includes joining the plurality of stator laminations as stacked in the sequence.

TECHNICAL FIELD

This relates generally to powertrains for electric vehicles, including amotor of an electric vehicle having a stator and a rotor and methods andsystems for cooling the stator.

BACKGROUND

The powertrain of an electric vehicle includes a battery, an inverter, amotor, and a gearbox. The motor of an electric vehicle typicallyincludes a rotor and a stator. The efficiency of the motor is based inpart on maintaining a cool temperature of the stator.

SUMMARY

In some implementations, a method of fabricating a stator for anelectric motor includes providing a plurality of stator laminations andstacking the plurality of stator laminations in a sequence along anaxis. Each stator lamination of the plurality of stator lamination is acopy of the same stator lamination pattern. The stacking comprisesperiodically varying rotational orientations of the stator laminationswith respect to the axis. The method further includes joining theplurality of stator laminations as stacked in the sequence.

In some implementations, an electric motor includes a rotor having arotor shaft disposed along an axis of the rotor and a stator thatincludes a plurality of stator laminations stacked coaxially with therotor shaft in a sequence. Each stator lamination of the plurality ofstator laminations is a copy of the same stator lamination pattern. Thestator laminations have periodically varying rotational orientations ofthe stator laminations in the sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described implementations,reference should be made to the Detailed Description below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIGS. 1A, 1B and 1C are views of a casting of an electric vehicle, inaccordance with some implementations.

FIG. 2 is a cross-sectional view showing components within the casting,in accordance with some implementations.

FIG. 3 is a perspective view of components within the casting, but withthe casting omitted for visual clarity, in accordance with someimplementations.

FIG. 4 illustrates a stator lamination pattern with fins, in accordancewith some implementations.

FIG. 5 is a partial perspective view of stacked stator laminations withfins, in accordance with some implementations.

FIG. 6 is a partial view of a plurality of stator laminations with amanifold, in accordance with some implementations.

FIG. 7 illustrates a stator lamination pattern with apertures, inaccordance with some implementations.

FIG. 8 illustrates a plurality of stacked stator laminations withapertures, in accordance with some implementations.

FIG. 9 is a cut-away perspective diagram illustrating stacked statorlaminations with apertures, in accordance with some implementations.

Like reference numerals refer to corresponding parts throughout thedrawings and specification. Like fill patterns indicate correspondingparts throughout the drawings.

DETAILED DESCRIPTION

In some implementations, an electric motor includes a rotor and astator. The stator includes a plurality of stator laminations. Thestator laminations are all produced using the same pattern. These statorlaminations can be stamped, using the pattern, from an iron alloymaterial with a thickness of, for example, 0.25-0.35 mm. Thus, eachstator lamination has two faces (front and back) and an edge. The statorlaminations are stacked face-to-face to create the stator. Each statorlamination in the stack is electrically isolated from the other statorlaminations in the stack to avoid eddy current loss. To cool the stator,a cooling fluid (such as oil) is pumped through channels along thestack.

However, when the stator laminations are stacked in the same manner(e.g., one on top of the next, with no rotation between them), the oilin the channels passes over only the edge of each stator lamination andthus interacts with only a small surface area of each stator lamination,resulting in inefficient cooling.

Some implementations described herein solve this problem by rotatingstator laminations relative to each other (e.g., rotating the statorlaminations by 180 degrees about the axis of the rotor or flipping thelaminations over with respect to one another). The stator laminationpattern is designed such that, when stacked in this manner, the statorlaminations create channels as wells as regions in which the coolingfluid is forced against portions of the faces of the stator laminations.This is achieved, for example, by having fins that are stackedalternately relative to one another, or by having overlapping aperturesthat are stacked alternately relative to one another.

The increased surface area provided by the portions of the faces of thestator laminations with which the cooling fluid interacts results moreefficient cooling, which in turn increases the efficiency of theelectric motor.

Reference will now be made in detail to implementations, examples ofwhich are illustrated in the accompanying drawings. In the followingdetailed description, numerous specific details are set forth in orderto provide a thorough understanding of the various describedimplementations. However, it will be apparent to one of ordinary skillin the art that the various described implementations may be practicedwithout these specific details. In other instances, well-known methods,procedures, components, circuits, and networks have not been describedin detail so as not to unnecessarily obscure aspects of theimplementations.

Many modifications and variations of this disclosure can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific implementations described herein areoffered by way of example only, and the disclosure is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

FIGS. 1A-1C are views of a casting 1400 for an electric vehicle inaccordance with some implementations. The side view of FIG. 1B isopposite to the side view of FIG. 1A. In some implementations, thecasting houses an electric motor, gearbox and/or an inverter. As shownin FIGS. 1C and 2, the casting 1400 may include a first portion 1400Aand a second portion 1400B that are joined (e.g., bolted together) usingbosses 1402 (FIG. 1B and FIG. 2) during assembly, to encase componentswithin the casting 1400. The casting 1400 may be manufactured by diecasting and may be aluminum. FIG. 1B illustrates oil pump 1430 in alower corner of the casting such that an oil loop is created to cool themotor (e.g., motor 1406). In some implementations, the oil loop geometry(e.g., including the location of the oil pump to the inlet of thestator) is independent of the drive unit angle (e.g., the angle at whichthe drive unit is installed).

FIG. 2 is a cross-sectional view showing components within the casting1400 in accordance with some implementations. These components includean inverter 1404, electric motor 1406, and gearbox 1416. The inverter1404 receives DC power from a battery external to the casting 1400 andconverts the DC power to AC power, which is provided to the motor 1406.The motor 1406 includes a rotor 1412 disposed at least partially withina stator 1408. In some implementations, the stator 1408 includes aplurality of stator laminations (e.g., as described with reference toFIGS. 5-9) stacked coaxially with a rotor shaft 1414 in a sequence(e.g., along an axis about which the rotor 1412 and the rotor shaft 1414rotate). The stator 1408 has associated stator windings 1410, to whichthe AC power from the inverter 1404 is provided, at both ends. Thestator windings 1410 are thus electrically coupled to the output (e.g.,phase-out bus bars) of the inverter 1404; in this manner, the inverter1404 is coupled to the motor 1406 to provide the AC power to the motor1406. The rotor shaft 1414 extends beyond one end of the stator 1408.The gearbox 1416 includes a gear 1418 (FIG. 3) on the rotor shaft 1414,intermediate gearing 1420, and a final gear 1422 (e.g., a differentialgear). The intermediate gearing 1420 couples the rotor shaft 1414 withthe final gear 1422. The rotor shaft 1414 is situated between theinverter 1404 and components of the gearbox 1416, including theintermediate gearing 1420 and final gear 1422 but excluding the gear1418, as shown. A portion of the intermediate gearing 1420 (e.g., aportion of the gear 1424, FIG. 3), however, may overlap the rotor shaft1414, as shown.

FIG. 3 is a perspective view of components within the casting 1400situated at their positions within the casting 1400, but with thecasting 1400 omitted for visual clarity, in accordance with someimplementations. The gear 1418 is axially mounted on the rotor shaft1414 (i.e., the gear 1418 is connected to and concentric with the rotorshaft 1414). The intermediate gearing 1420 (FIG. 2) includes gears 1424and 1426 mounted axially and spaced apart on a shaft 1421 (i.e., thegears 1424 are connected to, concentric with, and spaced apart on theshaft 1421). The shaft 1421 is situated on a side of the rotor shaft1414 opposite to the inverter 1404 (i.e., the inverter 1404 is on afirst side of the rotor shaft 1414 and the shaft 1421 is on a secondside of the rotor shaft 1414 opposite to the first side; these sides maybe defined as opposite sides of a plane passing through the rotor shaft1414, such as the plane corresponding to the center line of the rotorshaft 1414 shown in FIG. 3). The gear 1424 engages with the gear 1418(i.e., teeth of the gear 1424 engage with teeth of the gear 1418). Thegear 1426 engages with the final gear 1422 (i.e., teeth of the gear 1426engage with teeth of the gear 1422). The final gear 1422 may beconnected to an axle 1428, such that the gearbox 1416 allows the motor1406 to rotate the axle 1428 and thereby provide drive. The axle 1428 issituated on a side of the rotor shaft 1414 opposite to the inverter 1404(i.e., the inverter 1404 is on a first side of the rotor shaft 1414 andthe axle 1428 is on a second side of the rotor shaft 1414 opposite tothe first side; these sides may again be defined as opposite sides of aplane passing through the rotor shaft 1414, such as the planecorresponding to the center line of the rotor shaft 1414 shown in FIG.3).

A method of fabricating a stator (e.g., stator 1408) for an electricmotor (e.g., motor 1406) is provided. In some implementations, themethod includes providing a plurality of stator laminations. Each statorlamination of the plurality of stator laminations is a copy of the samestator lamination pattern (e.g., stator lamination pattern 400 shown inFIG. 4 or stator lamination pattern 700 shown in FIG. 7). For example,using the same stator lamination allows for efficient manufacturingwithout increasing cost.

In some implementations, each stator lamination in the stack iselectrically isolated from the other stator laminations in the stack toavoid eddy current loss. In some implementations, the stator isfabricated to allow cooling of the stator temperature.

In some implementations, the method further includes stacking theplurality of stator laminations in a sequence along an axis, includingperiodically varying rotational orientations of the stator laminationsin the sequence. For example, the stator 1408 may include a plurality ofstator laminations stacked on top of each other. In someimplementations, while varying the rotational orientations of the statorlaminations in the sequence, the slots (e.g., slots 412 or slots 712) ofeach stator lamination of the plurality of stator laminations remainaligned with the slots of successive stator laminations in the stack. Insome implementations, each stator lamination of the plurality of statorlaminations is manufactured by stamping the same stator laminationpattern and assembling the plurality of stator laminations byalternating the positioning of the laminations (e.g., using openings 410and 710, discussed below).

It should be noted, however, that in some implementations, the methodincludes providing and stacking additional stator laminations beyondthat plurality of stator laminations (e.g., besides those that aremanufactured by stamping the same stator lamination pattern andassembling the plurality of stator laminations by alternating thepositioning of the laminations).

In some implementations, each stator lamination has a thickness between0.25-0.35 mm. In some implementations, over 400 stator laminations arestacked in order to form the stator. The total number of statorlaminations in the stack and the thickness of each lamination may varybased on manufacturing tolerances. In some implementations, the statorlaminations are made of an iron alloy material. In some implementations,the stator laminations are made of iron or aluminum.

In some implementations, periodically varying the rotationalorientations includes alternating the rotational orientations ofsuccessive stator laminations in the sequence by 180 degrees. Forexample, a stator lamination aligned in the first orientation “A” issuccessively followed by a stator lamination aligned in a secondorientation “B” (e.g., where the second orientation corresponds to a 180degree shift of the first orientation). Thus, in some implementations,an “A B A B A B . . . ” pattern is created for the orientations ofsuccessive laminations.

In some implementations, periodically varying the rotationalorientations includes alternating the rotational orientations ofsuccessive groups of stator laminations in the sequence by 180 degrees,wherein the rotational orientations of the stator laminations in eachgroup are identical. In some implementations, the successive groups aresuccessive pairs. In some implementations, the rotational orientationsof the two stator laminations in each pair are identical. For example, afirst group of stator laminations corresponding to a plurality of statorlaminations aligned in the first orientation “A” is successivelyfollowed by a second group of stator laminations corresponding to aplurality of stator laminations aligned in a second orientation “B.” Forexample, if the first group of stator laminations aligned in the firstorientation “A” includes three stator laminations and the second groupof stator laminations aligned in the second orientation “B” includesthree stator laminations, an “A A A B B B A A A B B B . . . ” patternmay be formed. It is to be understood that the number of statorlaminations in each successive group may vary. Each respective group ofthe successive groups may (e.g., or may not) have the same number oflaminations in the group.

FIG. 4 illustrates a perspective view of a stator lamination patternhaving fins, in accordance with some implementations. In someimplementations, the stator lamination pattern (e.g., stator laminationpattern 400) includes a plurality of fins 402 (e.g., including fin402-a, fin 402-b, fin 402-c, fin 402-d, fin 402-e, and fin 402-f) (theadditional fins shown in FIG. 4 are not labeled) along the circumferenceof the stator lamination pattern. In some implementations, the pluralityof fins 402 are arranged on the outer circumference of the statorlamination pattern and the fins are equally spaced. In someimplementations, the fins allows for better cooling than a statorlamination pattern without fins by increasing the surface area (e.g.,for oil to travel on) between successive stator laminations in thestack.

In some implementations, the stator lamination pattern 400 includes weldpoints 406 (e.g., including weld points 406-a, 406-b, and 406-c). Insome implementations, the weld points 406 of the stator laminations inthe sequence align regardless of the rotational orientations during thestacking. In some implementations, at least one of the weld points mayoverlap with a fin.

In some implementations, the stator lamination pattern 400 includes afirst opening 410 and a second opening 410. In some implementations, thefirst opening 410 (e.g., and/or the second opening 410) is in arespective fin. In some implementations, the first opening 410 and thesecond opening 410 are rotationally situated 180 degrees apart. In someimplementations, the first opening 410 and the second opening 410 areused as guide holes to align and/or rotate a plurality of statorlaminations (e.g., or groups of stator laminations). For example,successive stator laminations (or successive groups of statorlaminations) may be rotated (e.g., by 180 degrees) by matching the firstopening of a first stator lamination (or first group of laminations)with a second opening of a second stator lamination (or second group oflaminations). In some implementations, the stator lamination pattern 400may include more than two openings (e.g., a third opening, a fourthopening, etc.) used to align the plurality of stator laminations.Additional openings (e.g., in addition to the first opening and thesecond opening) may allow the plurality of stator laminations to berotated by less than 180 degrees.

In some implementations, first opening 410 includes an inlet for oil toenter and second opening 410 includes an outlet for oil to escape. Insome implementations, first opening 410 includes an outlet and secondopening 410 includes an inlet. In some implementations, first opening410 and second opening 410 perform the same functions as first opening710 and second opening 710, respectively, as described below withrespect to FIG. 7.

FIG. 5 is a partial side view of a plurality of stacked statorlaminations with fins. The method of fabricating the stator (e.g.,stator 1408) further includes stacking the plurality of statorlaminations in a sequence along an axis. For example, in FIG. 4, theaxis is along the z-plane traveling through the lamination. In someimplementations, the centers of respective stator laminations in thestack of the plurality of stator laminations are aligned.

The stacking of the plurality of stator laminations includesperiodically varying rotational orientations of the stator laminationsin the sequence, the rotational orientations being defined with respectto the axis. As shown in FIG. 5, the fins 402 of each successive statorlamination (e.g., or group of stator laminations) do not align. Thisresults in the gaps, shown in FIG. 5, between stator lamination fins.The weld points 406 of each successive stator lamination (e.g., or groupof stator laminations) are aligned (e.g., including weld points 406-a,406-b, 406-c) regardless of the rotational orientation of the respectivestator lamination (e.g., with respect to the axis).

In some implementations, periodically varying the rotationalorientations includes alternating the rotational orientations of statorlaminations in the sequence by 180 degrees. In some implementations,respective fins are situated directly opposite to respective portions ofthe circumference that do not include fins. For example, as shown byline 404 of FIG. 4, fin 402-a is situated directly opposite to a portionof the circumference that does not include fins (e.g., the portion ofthe circumference between fins 402-c and 402-d). The stator laminationpattern in FIG. 4 also shows that fin 402-b is situated directlyopposite to a portion of the circumference that does not include fins(e.g., the portion of the circumference between fins 402-e and 402-f).Therefore, when the rotational orientation of a second stator laminationis shifted (e.g., alternated) by 180 degrees with respect to therotational orientation of a first stator lamination, the fins of thesecond stator lamination do not directly align with the fins of thefirst stator lamination when stacked (e.g., with the stator laminationcenters aligned). In some implementations, the fins of successive statorlaminations (e.g., or stator lamination groups) do not overlap. Forexample, as shown in FIG. 6, there is a gap 602, between a first fin402-a, of a first stator lamination, and a second fin 402-b, of a secondstator lamination (e.g., where the second stator lamination is stackedbehind the first stator lamination and the fins of the first and secondstator laminations do not overlap).

FIG. 6 illustrates a partial view of at least two stator laminationshaving fins, the two stator laminations stacked, including a firststator lamination having a first rotational orientation and a secondstator lamination having a second rotational orientation (e.g., shiftedby 180 degrees). For example, the first stator lamination appears infront of the second lamination, which is stacked such that the centersof the two stator laminations align.

In some implementations, a manifold 600 wraps around the circumferenceof the stacked stator laminations. Manifold 600 may be used to force asubstance (e.g., a fluid such as oil) to pass between fins 402 of theplurality of stator laminations. In some implementations, the manifoldis a sealed manifold around the stator to create a closed oil loop. Insome implementations, manifold 600 is made of plastic or metal. In someimplementations, oil (e.g., or another substance) may be dripped ontothe outside of stator 1408 such that the oil travels between fins 402 ofthe plurality of stator laminations (e.g., without a manifold). In someimplementations, the oil travels between gaps 602.

FIG. 7 illustrates a perspective view of a stator lamination patternwith apertures, in accordance with some implementations. In someimplementations, the stator lamination pattern 700 includes a series ofapertures 704 (e.g., including aperture 704-a, aperture 704-b, aperture704-c) situated circumferentially around the stator lamination pattern.The apertures of adjacent (e.g., successive) stator laminations (e.g.,in the stack of stator laminations) with varying rotational orientationsin the sequence align to form channels. For example, as the rotationalorientations of the stator laminations change while stacking theplurality of stator laminations, the apertures of adjacent statorlaminations in the stack align, at least in part, to create channelsthat would allow a substance (e.g., a fluid such as oil) to flow throughthe channels (e.g., and travel over the complete surface area). In someimplementations, a greater number of stator laminations in eachsuccessive group corresponds with the creation of a larger channel. Insome implementations, the channels are sealed oil channels.

In some implementations, the stator lamination pattern 700 includes weldpoints 706 (e.g., including weld points 706-a, 706-b, and 706-c). Insome implementations, the weld points 706 align regardless of therotational orientations during the stacking. For example, while theapertures of adjacent stator laminations do not directly align (e.g.,but only partially overlap), the weld points 706 of adjacent statorlaminations align despite the change in rotational orientations betweenadjacent stator laminations.

In some implementations, the stator lamination pattern 700 includes afirst opening 710 and a second opening 710. In some implementations, thefirst opening 710 is in a respective aperture of the series of apertures704. In some implementations, the second opening 710 is separate fromthe series of apertures 704. In some implementations, the channels(e.g., created by the apertures of adjacent stator laminations) connectthe first opening 710 (e.g., of a first stator lamination in the stack)with the second opening 710 (e.g., of a second stator lamination in thestack). In some implementations, the first opening 710 and the secondopening 710 are rotationally situated 180 degrees apart.

FIG. 8 illustrates a plurality of stacked stator laminations (e.g.,including stator laminations 700-a and 700-b based on the statorlamination pattern 700) in a sequence along an axis (e.g., an axis thatis coaxial with a rotational axis of a rotor, FIG. 1). Each statorlamination 700 of the plurality of stator laminations is a copy of thesame stator lamination pattern. The stacking includes periodicallyvarying rotational orientations of the stator laminations in thesequence. In some implementations, the rotational orientations aredefined with respect to the axis (e.g., the rotations are periodicallyvaried by rotating the stator laminations, relative to one another, withrespect to the axis). In some implementations, the rotationalorientations are defined with respect to an axis in the plane of thestator laminations (e.g., the stator laminations are flipped overrelative to one another).

FIG. 9 is a negative-space representation of the stacked plurality ofstator laminations. As shown in the figure, the apertures 704 (e.g.,including apertures 704-b and 704-c) create channels that connect thefirst opening 710 with the second opening 710. For example, the channels(e.g., apertures) are shown as solid blocks (because FIG. 9 is anegative space representation). In some implementations, the stack ofthe stator laminations also forms regions in which a cooling fluid isforced against (e.g., applied to or incident upon) portions ofrespective faces of the stator laminations. In some implementations, theregions in which the cooling fluid is forced against the portions of therespective faces of the stator laminations are disposed between adjacentchannels (e.g., a region in which the cooling fluid is forced against aportion of a respective face is connected to a channel on each side ofthe region).

In some implementations, the stacking includes using the first opening710 and the second opening 710 as guide holes. For example, in FIG. 8,two successive stator laminations, 700-a and 700-b (e.g., each statorlamination having the stator lamination pattern 700 shown in FIG. 7),are illustrated as being rotated in the sequence by 180 degrees. Thefirst opening 710 (e.g., within an aperture) of stator lamination 700-ais aligned with the second opening 710 (e.g., not within an aperture) ofstator lamination 700-b. The stator laminations 700-a and 700-b arestacked over a plurality of additional stator laminations, eachadditional stator lamination also having the stator lamination pattern700.

In some implementations, the stator fabricated by stacking a pluralityof stators having the stator lamination pattern 700 allows for coolingof the drive unit regardless of the drive unit rotation (e.g., angledpositioning), as described above with reference to FIG. 1B. In someimplementations, an oil loop is created to allow oil to travel in bothdirections around the stator.

In some implementations, a manifold is disposed on the outside of thestack of stator laminations, as described as manifold 600 with respectto FIG. 6. In some implementations, the manifold pushes (e.g., contains)the fluid (e.g., oil) in the stack of stator laminations. In someimplementations, oil (e.g., or another substance) may be dripped onto aninlet (e.g., an oil pump inlet), such as the first opening 710 (e.g., orsecond opening 710) such that the oil travels, through the channels, inboth directions (e.g., clockwise and counterclockwise) across thesurface area of the stator lamination and flows out of an outlet, suchas the second opening 710 (e.g., or first opening 710). In someimplementations, an oil pump (e.g., oil pump 1430 of FIG. 1B) is locatedin a lower corner of casting 1400. In some implementations, the locationof the oil pump inlet allows for an oil loop to be created regardless ofthe angle of installation. For example, by allowing the oil to travelboth directions through the channels of the stator, the same drive unit(e.g., casting 1400) may be used in both the front and the rear of avehicle despite having different mounting angles, while maintaining thecooling of the drive unit.

In some implementations, the method of fabricating the stator furtherincludes joining the plurality of stator laminations as stacked in thesequence. In some implementations, the joining includes welding theplurality of stator laminations together at least one of the weld points(e.g., weld points 406 or weld points 706). In some implementations,joining the plurality of stator laminations includes welding theplurality of stator laminations together at multiple weld points 406(e.g., or weld points 706) along the circumferences of the statorlaminations. In some implementations, as explained above with respect toweld points 406 and 706, the weld points of the stator laminations alignregardless of the rotational orientations during the stacking.

In some implementations, joining the plurality of stator laminationsincludes connecting the plurality of stator laminations using epoxy. Itwill be understood that other joining agents may be used to join theplurality of stator laminations as stacked in the sequence.

It should be noted that the stators described herein may includeadditional stator laminations that are manufactured using the samepattern as the other stator laminations. For example, the phrase “eachstator lamination of the plurality of stator laminations is a copy ofthe same stator lamination pattern” does not imply the absence ofadditional stator laminations that are not a copy of the same statorlamination pattern. Instead, the phrase means that there are at leasttwo stator laminations that are a copy of the same stator laminationpattern.

It will also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are only usedto distinguish one element from another. For example, a first statorlamination could be termed a second stator lamination, and, similarly, asecond stator lamination could be termed a first stator lamination,without departing from the scope of the various describedimplementations. The first stator lamination and the second statorlamination are both stator laminations, but they are not the same statorlamination unless explicitly stated as such.

The terminology used in the description of the various describedimplementations herein is for the purpose of describing particularimplementations only and is not intended to be limiting. As used in thedescription of the various described implementations and the appendedclaims, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

As used herein, the term “if” is, optionally, construed to mean “when”or “upon” or “in response to determining” or “in response to detecting”or “in accordance with a determination that,” depending on the context.Similarly, the phrase “if it is determined” or “if [a stated conditionor event] is detected” is, optionally, construed to mean “upondetermining” or “in response to determining” or “upon detecting [thestated condition or event]” or “in response to detecting [the statedcondition or event]” or “in accordance with a determination that [astated condition or event] is detected,” depending on the context.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific implementations. However, theillustrative discussions above are not intended to be exhaustive or tolimit the scope of the claims to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The implementations were chosen in order to best explain theprinciples underlying the claims and their practical applications, tothereby enable others skilled in the art to best use the implementationswith various modifications as are suited to the particular usescontemplated.

What is claimed is:
 1. A method of fabricating a stator for an electricmotor, comprising: providing a plurality of stator laminations, whereineach stator lamination of the plurality of stator laminations is a copyof the same stator lamination pattern, wherein: the stator laminationpattern comprises a series of apertures situated circumferentiallyaround the stator lamination pattern, the series of apertures comprisingaxially elongated openings along the outer circumference of the statorlamination, the axially elongated openings are arranged in the series tobe radially asymmetric, wherein a center of a first aperture is situatedalong the outer circumference directly opposite to a portion of theouter circumference that does not include an aperture, and the axiallyelongated openings, when stacked, at least partially overlap; stackingthe plurality of stator laminations in a sequence along an axis,comprising periodically varying rotational orientations of the statorlaminations in the sequence; and joining the plurality of statorlaminations as stacked in the sequence.
 2. The method of claim 1,wherein the rotational orientations are defined with respect to theaxis.
 3. The method of claim 1, wherein periodically varying therotational orientations of the stator laminations in the sequencecomprises flipping the stator laminations by 180 degrees.
 4. The methodof claim 1, wherein periodically varying the rotational orientationscomprises alternating the rotational orientations of successive statorlaminations in the sequence by 180 degrees.
 5. The method of claim 1,wherein periodically varying the rotational orientations comprisesalternating the rotational orientations of successive groups of statorlaminations in the sequence by 180 degrees, wherein the rotationalorientations of the stator laminations in each group are identical. 6.The method of claim 5, wherein the successive groups comprise successivepairs, wherein the rotational orientations of the two stator laminationsin each pair are identical.
 7. The method of claim 1, wherein: theapertures of adjacent stator laminations with varying rotationalorientations in the sequence align to form channels.
 8. The method ofclaim 7, wherein: the stator lamination pattern comprises a firstopening and a second opening, the first opening being in a respectiveaperture of the series of apertures; the second opening being separatefrom the series of apertures; and the channels connect the first openingwith the second opening when the plurality of stator laminations isstacked in the sequence.
 9. The method of claim 8, wherein the stackingcomprises using the first opening and the second opening as guide holes.10. The method of claim 1, wherein joining the plurality of statorlaminations comprises welding the plurality of stator laminationstogether at multiple weld points along a circumferences of the statorlaminations.
 11. The method of claim 1, wherein joining the plurality ofstator laminations comprises connecting the plurality of statorlaminations using epoxy.
 12. An electric motor, comprising: a rotorhaving a rotor shaft disposed along an axis of the rotor; and a statorthat includes a plurality of stator laminations stacked coaxially withthe rotor shaft in a sequence, wherein: each stator lamination of theplurality of stator laminations is a copy of the same stator laminationpattern, wherein: the stator lamination pattern comprises a series ofapertures situated circumferentially around the stator laminationpattern, the series of apertures comprising axially elongated openingsalong the outer circumference of the stator lamination, the axiallyelongated openings are arranged in the series to be radially asymmetric,wherein a center of a first aperture is situated along the outercircumference directly opposite to a portion of the outer circumferencethat does not include an aperture, and the axially elongated openings,when stacked, at least partially overlap; and the stator laminationshave periodically varying rotational orientations of the statorlaminations in the sequence.
 13. The electric motor of claim 12,wherein: the apertures of adjacent stator laminations with varyingrotational orientations in the sequence overlap to form channels. 14.The electric motor of claim 12, wherein a first lamination has arotational orientation that is flipped with respect to a rotationalorientation of a second lamination.
 15. The electric motor of claim 12,wherein a first lamination has a rotational orientation that is rotated180 degrees about the axis relative to a second lamination.
 16. Theelectric motor of claim 12, wherein the stacking of the statorlaminations forms channels as wells as regions in which a cooling fluidis forced against portions of respective faces of the statorlaminations.